Yet again - this is very old fashioned language. Where are you getting these phrases from? The literal meaning is that you have done me a favour, by you being present again. In other words - I really appreciate that you visited me again. These days, since it is such formal and old-fashioned language, it is more likely to be used in a sarcastic manner, to mean the complete opposite!

I agree with Gary (yet again). Literally, this means 'I'm glad to see you again'. But the language is extremely formal and outdated, and you should only interpret it as meaning 'I'm glad to see you again' if you come across the sentence in a conversation written or set over a hundred years ago. If someone says this in a modern setting, they are being sarcastic. A typical example might be if a very lazy employee hasn't shown up at work for several weeks. When they finally do come to work, the boss might say something like this.